CA1305445C - Process for the continuous separation of water from mixtures with organic substances - Google Patents
Process for the continuous separation of water from mixtures with organic substancesInfo
- Publication number
- CA1305445C CA1305445C CA000530570A CA530570A CA1305445C CA 1305445 C CA1305445 C CA 1305445C CA 000530570 A CA000530570 A CA 000530570A CA 530570 A CA530570 A CA 530570A CA 1305445 C CA1305445 C CA 1305445C
- Authority
- CA
- Canada
- Prior art keywords
- water
- column
- separation
- distillation
- mixtures
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired - Fee Related
Links
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 title claims abstract description 194
- 239000000203 mixture Substances 0.000 title claims abstract description 36
- 238000000926 separation method Methods 0.000 title claims abstract description 35
- 238000000034 method Methods 0.000 title claims abstract description 17
- 230000008569 process Effects 0.000 title claims abstract description 16
- 239000000126 substance Substances 0.000 title abstract description 29
- 238000004821 distillation Methods 0.000 claims abstract description 40
- BZLVMXJERCGZMT-UHFFFAOYSA-N Methyl tert-butyl ether Chemical compound COC(C)(C)C BZLVMXJERCGZMT-UHFFFAOYSA-N 0.000 claims description 53
- 239000012071 phase Substances 0.000 claims description 39
- 238000010992 reflux Methods 0.000 claims description 20
- 238000009834 vaporization Methods 0.000 claims description 17
- 230000008016 vaporization Effects 0.000 claims description 17
- 230000015572 biosynthetic process Effects 0.000 claims description 11
- 238000001035 drying Methods 0.000 claims description 9
- 229930195733 hydrocarbon Natural products 0.000 claims description 6
- 150000002430 hydrocarbons Chemical class 0.000 claims description 6
- 239000007791 liquid phase Substances 0.000 claims description 6
- 239000007788 liquid Substances 0.000 claims description 3
- 125000002496 methyl group Chemical group [H]C([H])([H])* 0.000 claims description 3
- 239000004215 Carbon black (E152) Substances 0.000 claims description 2
- 238000004508 fractional distillation Methods 0.000 claims description 2
- 238000005191 phase separation Methods 0.000 claims description 2
- AQEFLFZSWDEAIP-UHFFFAOYSA-N di-tert-butyl ether Chemical compound CC(C)(C)OC(C)(C)C AQEFLFZSWDEAIP-UHFFFAOYSA-N 0.000 claims 1
- 238000009835 boiling Methods 0.000 abstract description 16
- 238000000746 purification Methods 0.000 abstract description 3
- BTANRVKWQNVYAZ-UHFFFAOYSA-N butan-2-ol Chemical compound CCC(C)O BTANRVKWQNVYAZ-UHFFFAOYSA-N 0.000 description 72
- ZWEHNKRNPOVVGH-UHFFFAOYSA-N 2-Butanone Chemical compound CCC(C)=O ZWEHNKRNPOVVGH-UHFFFAOYSA-N 0.000 description 64
- 239000000047 product Substances 0.000 description 55
- VLKZOEOYAKHREP-UHFFFAOYSA-N n-Hexane Chemical compound CCCCCC VLKZOEOYAKHREP-UHFFFAOYSA-N 0.000 description 18
- DKGAVHZHDRPRBM-UHFFFAOYSA-N Tert-Butanol Chemical compound CC(C)(C)O DKGAVHZHDRPRBM-UHFFFAOYSA-N 0.000 description 15
- 239000006227 byproduct Substances 0.000 description 15
- 238000002474 experimental method Methods 0.000 description 12
- 239000000243 solution Substances 0.000 description 11
- HHBZZTKMMLDNDN-UHFFFAOYSA-N 2-butan-2-yloxybutane Chemical compound CCC(C)OC(C)CC HHBZZTKMMLDNDN-UHFFFAOYSA-N 0.000 description 9
- OKKJLVBELUTLKV-UHFFFAOYSA-N Methanol Chemical compound OC OKKJLVBELUTLKV-UHFFFAOYSA-N 0.000 description 9
- 238000009833 condensation Methods 0.000 description 7
- 230000005494 condensation Effects 0.000 description 7
- VQTUBCCKSQIDNK-UHFFFAOYSA-N Isobutene Chemical compound CC(C)=C VQTUBCCKSQIDNK-UHFFFAOYSA-N 0.000 description 6
- 239000003795 chemical substances by application Substances 0.000 description 6
- 239000000539 dimer Substances 0.000 description 6
- 238000000354 decomposition reaction Methods 0.000 description 5
- XDTMQSROBMDMFD-UHFFFAOYSA-N Cyclohexane Chemical compound C1CCCCC1 XDTMQSROBMDMFD-UHFFFAOYSA-N 0.000 description 4
- LCGLNKUTAGEVQW-UHFFFAOYSA-N Dimethyl ether Chemical compound COC LCGLNKUTAGEVQW-UHFFFAOYSA-N 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 4
- 239000008346 aqueous phase Substances 0.000 description 4
- 239000012074 organic phase Substances 0.000 description 4
- 238000003786 synthesis reaction Methods 0.000 description 4
- UHOVQNZJYSORNB-UHFFFAOYSA-N Benzene Chemical compound C1=CC=CC=C1 UHOVQNZJYSORNB-UHFFFAOYSA-N 0.000 description 3
- 239000002904 solvent Substances 0.000 description 3
- RTZKZFJDLAIYFH-UHFFFAOYSA-N Diethyl ether Chemical compound CCOCC RTZKZFJDLAIYFH-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- IMNFDUFMRHMDMM-UHFFFAOYSA-N N-Heptane Chemical compound CCCCCCC IMNFDUFMRHMDMM-UHFFFAOYSA-N 0.000 description 2
- OFBQJSOFQDEBGM-UHFFFAOYSA-N Pentane Chemical compound CCCCC OFBQJSOFQDEBGM-UHFFFAOYSA-N 0.000 description 2
- CDBYLPFSWZWCQE-UHFFFAOYSA-L Sodium Carbonate Chemical compound [Na+].[Na+].[O-]C([O-])=O CDBYLPFSWZWCQE-UHFFFAOYSA-L 0.000 description 2
- 230000001174 ascending effect Effects 0.000 description 2
- 239000007795 chemical reaction product Substances 0.000 description 2
- 239000000356 contaminant Substances 0.000 description 2
- 230000001419 dependent effect Effects 0.000 description 2
- 238000004090 dissolution Methods 0.000 description 2
- 238000007700 distillative separation Methods 0.000 description 2
- 238000010981 drying operation Methods 0.000 description 2
- 235000019441 ethanol Nutrition 0.000 description 2
- 239000012535 impurity Substances 0.000 description 2
- 150000002500 ions Chemical class 0.000 description 2
- 238000004519 manufacturing process Methods 0.000 description 2
- 238000005406 washing Methods 0.000 description 2
- DURPTKYDGMDSBL-UHFFFAOYSA-N 1-butoxybutane Chemical compound CCCCOCCCC DURPTKYDGMDSBL-UHFFFAOYSA-N 0.000 description 1
- 206010013786 Dry skin Diseases 0.000 description 1
- 238000010533 azeotropic distillation Methods 0.000 description 1
- 239000003054 catalyst Substances 0.000 description 1
- 230000002844 continuous effect Effects 0.000 description 1
- 239000012043 crude product Substances 0.000 description 1
- 238000006356 dehydrogenation reaction Methods 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000008030 elimination Effects 0.000 description 1
- 238000003379 elimination reaction Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 230000036571 hydration Effects 0.000 description 1
- 238000006703 hydration reaction Methods 0.000 description 1
- 238000002955 isolation Methods 0.000 description 1
- 239000012263 liquid product Substances 0.000 description 1
- 239000000463 material Substances 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000003405 preventing effect Effects 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 238000005063 solubilization Methods 0.000 description 1
- 230000007928 solubilization Effects 0.000 description 1
- 230000002311 subsequent effect Effects 0.000 description 1
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D3/00—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping
- B01D3/34—Distillation or related exchange processes in which liquids are contacted with gaseous media, e.g. stripping with one or more auxiliary substances
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C29/00—Preparation of compounds having hydroxy or O-metal groups bound to a carbon atom not belonging to a six-membered aromatic ring
- C07C29/74—Separation; Purification; Use of additives, e.g. for stabilisation
- C07C29/76—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment
- C07C29/80—Separation; Purification; Use of additives, e.g. for stabilisation by physical treatment by distillation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C41/00—Preparation of ethers; Preparation of compounds having groups, groups or groups
- C07C41/01—Preparation of ethers
- C07C41/34—Separation; Purification; Stabilisation; Use of additives
- C07C41/40—Separation; Purification; Stabilisation; Use of additives by change of physical state, e.g. by crystallisation
- C07C41/42—Separation; Purification; Stabilisation; Use of additives by change of physical state, e.g. by crystallisation by distillation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
- C07C45/002—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds by dehydrogenation
-
- C—CHEMISTRY; METALLURGY
- C07—ORGANIC CHEMISTRY
- C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
- C07C45/00—Preparation of compounds having >C = O groups bound only to carbon or hydrogen atoms; Preparation of chelates of such compounds
- C07C45/78—Separation; Purification; Stabilisation; Use of additives
- C07C45/81—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation
- C07C45/82—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation by distillation
- C07C45/84—Separation; Purification; Stabilisation; Use of additives by change in the physical state, e.g. crystallisation by distillation by azeotropic distillation
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
- Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y10S203/00—Distillation: processes, separatory
- Y10S203/20—Power plant
Abstract
PROCESS FOR THE CONTINUOUS SEPARATION OF
WATER FROM MIXTURES WITH ORGANIC SUBSTANCES
(D#71,200-DTA-182 -F) ABSTRACT OF THE INVENTION
In the distillative purification or splittling-up of organic substances or mixtures of substances which have only limited capability of absorbing water and which, with water boil as azeotropes or,being not able to form azeotropes with water,boil higher than water, the water con-tained therein is continuously separated by effect-ing, in the distillation column, the separation of water under distillation conditions by the pre-sence of one or mor substances boiling overhead and reducing the capacity of taking in water in the organic substances or mixtures of substances to be purified, and by separating the nonvaporized water, wholly or in part, below the product feeding point already and withdrawing it at the side of the distillation column.
WATER FROM MIXTURES WITH ORGANIC SUBSTANCES
(D#71,200-DTA-182 -F) ABSTRACT OF THE INVENTION
In the distillative purification or splittling-up of organic substances or mixtures of substances which have only limited capability of absorbing water and which, with water boil as azeotropes or,being not able to form azeotropes with water,boil higher than water, the water con-tained therein is continuously separated by effect-ing, in the distillation column, the separation of water under distillation conditions by the pre-sence of one or mor substances boiling overhead and reducing the capacity of taking in water in the organic substances or mixtures of substances to be purified, and by separating the nonvaporized water, wholly or in part, below the product feeding point already and withdrawing it at the side of the distillation column.
Description
~ 3~S'~S
~' PROCESS FOR THE CONTINUOUS SEPARATION
OF WATER FROM MIXTURES WITH ORGANIC SUBSTANCES
(D#71,200 ~- DTA-182~F) BACKGROUND OF T~E INVENTION
1. Field of the Invention This invention relates to a process for the contin-uous separation of water during distillative purification or splitting-up of organic substances or mixtures of substances in a distillation column which contain water in a dissolved form, the organic substances or mixtures of substances hav-ing only limited capability of absorbing water and, with water boiling as azeotropes, or without the capability of forming azeotropes with water, boiling higher than water.
:
, It is known that in the distillativç splitting-up of mixtures of substances the presence of water involves considerable separation problems. This is particularly true if one of the components of the materials mixture is a solu-bilizer or water.
Such solubilizers for water are usually the pro-ducts contained in the distillation feed and to be purified during distillative separation. These products are always ~the hlghest boiling under distillation conditions and, consequently, these are also obtained in the sump of distill-ation column. Solubilizers for water, are for instance, ~ethyl tert-butyl èther, methyl ethyl keton and sec-butyl alcohol.
35 ~
:
' ~ .
~` 2. Disclosure Statement German Patent DE-OS 25 47 380, discloses a reac-tion product of the methyl tert-butyl ether (MTBE) synthesis which contains, besides C4-hydrocarbons, mainly MTBE and unreacted methanol and minor quantities of tert-butyl alcohol (TBA) and dimethylether (DME) is first subjected to washing with wa-ter in order to eliminated methanol. Thereby, due to solubilization of MTBE, water is transferred to the raffinate phase of the extractor that has been freed from methanol by washing.
The water content in this raffinate phase is dependent on the MTBE concentration which, in its turn, is dependent on the isobutene concentration in the C4-cut feedstock for the MTBE synthesis. At low isobutene concentrations, small amounts of MTBE are formed which, thus, solubilize only little water into the raffinate phase. This water, together with the relatively great quantity of inert C4-hydrocarbons, can be easily phased out azeotropically and withdrawn and can be separated when the latter products are separated from MTBE. At high isobutene concentrations, however, correspond-ingly great quantities of MTBE are formed which solubilize so much water into the raffinate phase that this may pos-sibly be no longer sufficiently phased out azeotropically together with the amount of inert C4-hydrocarbons during separation from MTBE. In this case, sufficient elimination of water can only be attained by correspondingly higher vaporization of C4-hydrocarbons (higher reflu~ing~, or subse-quent drying of the formed MTBE is necessary.
German ~atent DE-OS 23 47 097 discloses the pro-duction of methyl ethyl ketone (MEK) from water-containing sec-butyl alcohol (SBA~, be it by dehydrogenatlon or by oxidation, more or less water-containing crude products are obtained. According to the process described in ~ :
~' PROCESS FOR THE CONTINUOUS SEPARATION
OF WATER FROM MIXTURES WITH ORGANIC SUBSTANCES
(D#71,200 ~- DTA-182~F) BACKGROUND OF T~E INVENTION
1. Field of the Invention This invention relates to a process for the contin-uous separation of water during distillative purification or splitting-up of organic substances or mixtures of substances in a distillation column which contain water in a dissolved form, the organic substances or mixtures of substances hav-ing only limited capability of absorbing water and, with water boiling as azeotropes, or without the capability of forming azeotropes with water, boiling higher than water.
:
, It is known that in the distillativç splitting-up of mixtures of substances the presence of water involves considerable separation problems. This is particularly true if one of the components of the materials mixture is a solu-bilizer or water.
Such solubilizers for water are usually the pro-ducts contained in the distillation feed and to be purified during distillative separation. These products are always ~the hlghest boiling under distillation conditions and, consequently, these are also obtained in the sump of distill-ation column. Solubilizers for water, are for instance, ~ethyl tert-butyl èther, methyl ethyl keton and sec-butyl alcohol.
35 ~
:
' ~ .
~` 2. Disclosure Statement German Patent DE-OS 25 47 380, discloses a reac-tion product of the methyl tert-butyl ether (MTBE) synthesis which contains, besides C4-hydrocarbons, mainly MTBE and unreacted methanol and minor quantities of tert-butyl alcohol (TBA) and dimethylether (DME) is first subjected to washing with wa-ter in order to eliminated methanol. Thereby, due to solubilization of MTBE, water is transferred to the raffinate phase of the extractor that has been freed from methanol by washing.
The water content in this raffinate phase is dependent on the MTBE concentration which, in its turn, is dependent on the isobutene concentration in the C4-cut feedstock for the MTBE synthesis. At low isobutene concentrations, small amounts of MTBE are formed which, thus, solubilize only little water into the raffinate phase. This water, together with the relatively great quantity of inert C4-hydrocarbons, can be easily phased out azeotropically and withdrawn and can be separated when the latter products are separated from MTBE. At high isobutene concentrations, however, correspond-ingly great quantities of MTBE are formed which solubilize so much water into the raffinate phase that this may pos-sibly be no longer sufficiently phased out azeotropically together with the amount of inert C4-hydrocarbons during separation from MTBE. In this case, sufficient elimination of water can only be attained by correspondingly higher vaporization of C4-hydrocarbons (higher reflu~ing~, or subse-quent drying of the formed MTBE is necessary.
German ~atent DE-OS 23 47 097 discloses the pro-duction of methyl ethyl ketone (MEK) from water-containing sec-butyl alcohol (SBA~, be it by dehydrogenatlon or by oxidation, more or less water-containing crude products are obtained. According to the process described in ~ :
.
:
. , ~ , DE-OS 23 47 197, water contents of between 3 and 15 percent have to be expected. Expediently, such reaction products are first dried prior to isolation of MEK. Drying is usu-ally done with azeotropic entraining agents such as benzene, hexane, cyclohexane, heptane.
U.S. Patent 3,228,985, discloses a multistage process for purifying MEK in which the stream to be purified is first extractively distilled with sodium carbonate solu-tion, is then treated with pentane while an aqueous phase isformed, and the residual water of the organic phase is azeo-tropically distilled off. The utilities consumption of such azeotropic drying operations is mainly determined by the composition of the ternary azeotropes and their decomposi-tion into phases.
During conventional production of SBA by indirecthydration using, e.g., sulfuric acid as a catalyst, a water-containing crude alcohol is obtained.
Patent SpecificationsGB-PS 829 424, DE-OS 1_0_7 602, and DE-OS 2 033 707 disclose distillation procedures for the~purification of aqueous crude SBA. In these processes, the water contained in the crude alcohol is jointly separated with higher-boiling byproducts or impuri-ties in a separating column. Formation of azeotropes with water is then a basic prerequisite for the separability of byproducts or contaminants such as di-sec-butyl ether (DSBE) and C8-hydrocarbons from SBA. On the other hand, the water 30~ contained in the crude SBA, which itself forms an SBA-rich homogeneous azeotrope with SBA, can be separated with such byproducts from SBA without too great quantities of SBA
;~ ~ being phased out with the water from the SB~ to be purified.
A dry SBA is obtained.
35 ~
:
. , ~ , DE-OS 23 47 197, water contents of between 3 and 15 percent have to be expected. Expediently, such reaction products are first dried prior to isolation of MEK. Drying is usu-ally done with azeotropic entraining agents such as benzene, hexane, cyclohexane, heptane.
U.S. Patent 3,228,985, discloses a multistage process for purifying MEK in which the stream to be purified is first extractively distilled with sodium carbonate solu-tion, is then treated with pentane while an aqueous phase isformed, and the residual water of the organic phase is azeo-tropically distilled off. The utilities consumption of such azeotropic drying operations is mainly determined by the composition of the ternary azeotropes and their decomposi-tion into phases.
During conventional production of SBA by indirecthydration using, e.g., sulfuric acid as a catalyst, a water-containing crude alcohol is obtained.
Patent SpecificationsGB-PS 829 424, DE-OS 1_0_7 602, and DE-OS 2 033 707 disclose distillation procedures for the~purification of aqueous crude SBA. In these processes, the water contained in the crude alcohol is jointly separated with higher-boiling byproducts or impuri-ties in a separating column. Formation of azeotropes with water is then a basic prerequisite for the separability of byproducts or contaminants such as di-sec-butyl ether (DSBE) and C8-hydrocarbons from SBA. On the other hand, the water 30~ contained in the crude SBA, which itself forms an SBA-rich homogeneous azeotrope with SBA, can be separated with such byproducts from SBA without too great quantities of SBA
;~ ~ being phased out with the water from the SB~ to be purified.
A dry SBA is obtained.
35 ~
, :
:~ , ' ' . : ' ' - ~ . .. .
: - :
.
Therefore, from the composition of the ternary azeotropic mixture thus formed and the solubility product resulting from this heterogeneous ternary composition, the following alternative conditions for the distillation are inferred: either a sufficient amount of water for the sep-aration of the amount of azeotropically higher-boiling by-products entrained in the distillation or a sufficient amount of azeotropically higher-boiling byproducts for the separation of the amount of water entrained in the distill-ation has to be made available.
Patent Specification GB-PS 829 424 partic-ularly describes the problem of how, during the distillation of aqueous crude SB~, the water and azeotropically higher-boiling byproducts can be separated in a column by con-trolled refluxing of aqueous phase and organic phase from the overhead product separator while maintaining a stable equilibrium in the column.
These examples make clear that the separation of water from such or similar product systems always involves a considerable effort with respect to the apparatuses or the utilities consumption.
German Patent Specification 24 07 949 outlines the formation of binary and/or ternary azeotropic mixtures is usually made use of and it is unavoidable to perform the operation with reflux ratios adjusted to the removal of water, to use separate drying columns, or to carry out dry-ing with a mole sieve in the slipstream of the column.
Therefore, it is an object of the present inven-tion to develop easily feasible or less expensive separation processes which are particularly capable of simultaneously ; 35 separating byproducts or contaminants and water.
-~ - 4 -~ 70830-14 SUMMARY OF THE IN ENTION
According to the present invention, this problem of water separation is solved by effecting, under distillation conditions in the distillation column, the separation of water from the organic substances or mixtures of substances to be purified by utilizing the presence of one or more substances boiling overhead and reducing the capacity of taking in water in the organic substances or mixtures of substances to be purified such that the water, wholly or in part, separate as the non-vaporized below the product feeding point already and is with-drawing it at the side of the distillation column.
Thus, the substance or the substances boiling overhead reduce the dissolution of water in the organic substances of mixtures of substances to be purified, or form together with water only insufficient azeotropes and thus effect overstepping of the solution limit for water in the organic substances or mixtures of substances.
According to one aspect of the present invention there ; is provided in a process for the separation of methyl tert-butyl ether f.rom a mixture comprising methyl tert-butyl ether, water and C4 hydrocarbons by fractional distillation in a distillation ~ column having means for vaporization of liquid at the base of the :; column and means for condensing vapors passing overhead therefrom and for returning a portion of the resultant condensate to the : top of the column as reflux, the improvement which comprises: -(a) introducing a feed mixture comprising C4 hydrocarbons :
~ - 5 -,, :
.
.
' :~L~ d ~ S 7 0 8 3 0--14 and methyl tert~butyl ether containing dissolved water into the distillation column at a feed point intermediate the base and top of the column, (b) distilling C4 hydrocarbon overhead with entrained water vapor, (c) condensing the distillate vapors with the formation of two immisclble liquid phases comprising a first water-rich phase and a C4-rich phase, (d) returning a portion of the C4-rich phase to the top of the column as reflux, (e) collecting a second water-rich phase and an immiscible methyl tert-butyl ether-rich phase at a point in the column below the feed point and above the base of the column, (f) withdrawing the second water-rich phase from the distillation column, and (g~ recovering methyl tert-butyl ether substantially freed from dissolved water from the base of the column.
According to a further aspect of the present invention there is provided an apparatus for performing the process defined above which comprises a distillation column suitable for azeo-tropic drying, provided with a water separator with internal or external phase separation located below the feeding tray.
; DETAILED DESCRIP~ION OF THE INVENTION
._ _ The process relates to organic substances or mixtures of substances to be purified which have only limited capability ; ~ ~of taking in water. Due to the presence of one or more substances - 5a -. , :
:
-~5~5 70830-14 reducing the dissolution of water in the organic substances or mixtures of substances to he purified, the water is eliminated.
Such products limiting the solution are at first the products to be prepared in a pure form if by overstepping the solution limit for water the water is forced to separate. This, for instance, applies to the solution limit for water in MTBE.
The solution limit for water in the product to be produced is overstepped by the - 5b -: ' , .
]oint presence of high-boiling products in the distilla-tion feed pre-venting or limiting the entraining of water into the over-head product. 3ut products limiting the solution are also those products which are contained in a concentrated form in the high-boiling overhead product and which further reduce at a suitable point in the column (below the product feeding point) the solution limit for water in the product to be produced. Such products are, for instance, n-hexane that lower the solubility of water in methyl ethyl ketone and di-sec-butyl ether that lowers the solubility of water in sec-butyl alcohol.
According to the process of the present invention, a state of permanent water saturation is maintained in the column so that the water continuously entrained with the distillation feed is inevitably eliminated due to oversatu-ration and can be withdrawn nonvaporized.
After the separation of water in the column, the residual water content in -the outflowing liquid column pro-duct is always lower than the possible water content in the ascending vaporous column product so that automatically a dry product is warranted at the column sump.
hus it has been surprisingly found that when reversing the drying principle usually employed, vaporiza-tion with azeotrope formation and condensation with decompo-sition into phases and separation of water -- be-tter results are obtained.
According to the invention, the product composi-tion which is favorable, at this point, for the insolubility of water is utilized for separating and withdrawing water in the distillation column already and this always below the ~ .
~ ~ - 6 -, ~.. ..
product feeding point. Thus, formation of water azeotropes overhead of the column can be omitted or the amount of water azeotropes overhead of the column can be lowered.
The residual water content in the liquid product stream flowing out to the stripping section of the column which results from the solution equilibrium at this water separation point, is azeotropically refluxed to the column section above the water separation point by the organic vapors formed by vaporization and ascending in the stripping section. For this return transport of water on the basis of the individually possible azeotropic compositions, a vapori-zation effort is necessary that mostly results from the separation task overlapping with the separation of other impurities. Thus, no additional vaporization effort is required for the separation of water.
In those cases where solely the separation of water is necessary, the vaporization effort has only to be adjusted to the entraining of water and to the azeotropic properties in the stripping section of the column by a cor~
respondingly forced reflux to the column.
Moreover, also by deliberate and controlled water removal at the separating tray, the water concentration in the stripping section of the column can be adjusted and maintained as required for specific separation tasks.
Thus, it is possible to withdraw the water to be 30 separated from water containing organic mixtures, wholly or n part, without additional or with a considerably lower vaporization effort, at a water separator located below the feeding point in the distillat.ion column.
~- - 7 -I'he technical realization of the princlple of the invention can be achieved by boostering a distillation column which is particularly suitable for the azeotropic drying operation by an incorporated water separator. The water separator should be installed at the point where the highest water separation has to be expected. In any case, not higher than the feeding ray or shortly below.
In this connection, it is unimportant whether an external water separator outside the column or a water sep-arating tray inside the column, is conceived as the tech-nical solution. The important thing is that all of the product outflowing to the stripping section of the distilla-tion column is conducted via the water separator. sy this prerequisite of the invention, it is warranted that the entraining of water into the stripping section of the column can always be adjusted by the solubility product on the water separating tray, irrespective of the water concentra-tion in the feedstock.
The following examples illustrate the invention by means of FIGS. 1 and 2. The examples show that by the pro-cess of the invention a significant reduction of the distil-lation effort for the separation of water is achieved or an additional distillation effort for the separation of water exceeding the actual separation task is avoided.
:
In a continuously operated distillation column schematically depicted in fig. 1, a water-containing mixture of methyl tert-~utyl ether (MTBE) and C4-hydrocarbons at a ratio of 65:35 parts-by-weight was separated by distillation at a pressure of 6 bar. The product was fed via line 1 in ':
, - 8 -- :
'YL5 the lower part of the column, 15 trays above the column sump.
Water entrained in the column was azeotropically phased out via line 2 together with the C4-hydrocarbons as overhead product, was separated after condensation of the overhead product and was withdrawn from the reflux vessel via line 3. To keep up the separation of MTBE/C4-hydro-carbons part of the overhead product was refluxed to the column via line 4. The overhead product portion contained in the feedstock was withdrawn as a distillate via line 5.
Re reflux ration R/D substantially determining the utilities consumption during this distillation is calculated from the ratio of reflux (R) to distillate (D).
In the comparison experiments 1.1 and 1.2 it is shown that when considering the simultaneous drying of water-containing feed mixtures, this reflux ratio has to be raised, in unfavorable cases, to a higher ratio -then required for the separation of MTBE and C4-hydrocarbons.
EXPERIMENT 1.1 ( COMPARI S ON ) ~ith a water portion of 9.lg entrained in 1260g of feed mixture (equal to 0.72 wt.% water) 1280g of C4 overhead product with 9.70 wt.% water were distilled off from the column by a reflux of 860g and a R/D reflux ratio of 2Ø
From this overhead product, 9.0g of water could be separated and withdrawn as a liquid phase. In the column sump 830g of C4-free MTBE with a water content of less than 0.03 wt.%
were obtained via line 6.
_ 9 _ ~ 3S~
EXPERIMENT 1.2 (COMPARISON) With a water portion of 8.5g entrained in a 1260g of feed mi~ture (equal to 0.67 wt.% water) 970g of C4 over-head product with 0.57 wt.% water were distilled off by areflux of 540g and a R/D reflux ratio of 1.2. From this overhead product, 5.5g of water could be separated and with-drawn as a liquid phase. Due to the insufficient entraining power for water of the overhead product, 830g of c4-free MTBE with a water content of 0.7 wt.% were obtained in the column sump via line 6.
In contrast thereto, as schematically depicted in figure 1, the following results can be obtained according to the invention by incorporating a water separator at a suit-able point of the column below the feeding tray and by with-drawing water via line 7:
EXPERIMENT 1.3 ACCORDING TO THE PRESENT INVENTION
. .
With a water portion of 9.8g entrained in a 1400g of feed product (equal to 0.70 wt.% water) 740g of C4 over-head product with 0.51 wt.% wa-ter were distilled off by a reflux of 250g and a R//D reflux ratio of 0.5. From this overhead product, 3.6g of water could be separated and wlth-drawn as a liquid phase. At the water separator in the column, 6.lg of water could be withdrawn through line 7. In the column sump, 910g of C4~free MTBE with a water content of less than 0.02 wt.%, were obtained through line 6.
EXPERIMENT 1.4 (ACCORDING TO THE PRESE~T INVENTION
With a water portion of 35g entrained in 1400 g of feed product (equal to 2.4 wt.% water) 740g of C4 overhead product with 0.5 wt.% water were distilled off by a reflux of 250g and a R/D reflux ratio of 0.5. From this overhead product, 3.7g of water could be separated and withdrawn as a . ~, , liquid phase. At the water separator in the column, 31.3g of water could be withdrawn through line 7. In the column sump, 910g of C4-free MTBE, with a water content of less than 0.02 wt.%, were obtained through line 6.
A crude methyl ethyl ketone (MEK) which was, for instance, produced by dehydrogenation of water-containing sec-butyl alcohol (SBA) and which contains 10 wt.~ water due to its autosolubility for water, was to be dried. Since direct separation of MEK and water is impossible due to the azeotrope formation of MEK/water, drying was to be carried out according to the state-of-the-art by azeotropic distil-lation with suitable entraining agents in a continuousl~operated distillation column schematically depicted in fig-ure 2. As azeotropic entraining agents for water, for in-stance, n-hexane or cyclohexane are used.
When feeding l.Okg of crude, MEK with 10% = 0.lkg of water via line 11, the following results were obtained.
EXPERIMENT 2.1 (COMPARISON) Using n-hexane as the azeotropic entraining agent, 2.172kg of azeotropic overhead product with 68.1 wt.%
n-hexane, 27.1 wt.% MEK and 4.8 wt.% wa*er at 56C had to be produced by vaporization and had to be removed at the column head via line 12 in order to separate 0.lkg of water or to ~ ~ 30 produce 0.9kg of dry crude MEK. After condensation and decomposition into phases 0.113kg of heavy phase with 0.lkg of water was removed therefrom via line 13, whereas 2.059kgs of light phase were refluxed to the column via line 14. At the~column sump, dry crude MEK was withdrawn via line 16.
Line 15 was not used.
: ~ ' ~:
EXPERIMENT 2.2 (COMPARISON?
Using cyclohexane as -the azeotropic entraining agent, 1.33kg of azeotropic overhead product with 56.8 wt.~
cyclohexane, 35.2 wt.% MEK and 8.0 wt.% water at 64C had to be produced by vaporization and had to be removed at the column head via line 12 in order to separate 0.lkg of water or to produce 0.9kg of dry crude MEK. After condensation and decomposition into phases 0.115kg of heavy base with 0.lkg of water was removed therefrom via line 13, whereas 1.215kgs of light phase were refluxed to the column via line 14. At the column sump dry crude MEK was withdrawn via line 16. Line 15 was not used.
In contrast thereto, when using the process of the invention, the vaporization effort can be considerably lo-wered by removing the water via line 17. The quantity of entraining agent to be employed therefor is not determined as a function of the composition of the ternary azeotrope but by the solubility product at the water separator. How-ever, the entrainer recycle has to be at least so high that the dissolved water quantity entrained from the water separ-ator in the column (depending on the MEK/entrainer ratio) can be stripped from the column as MEK/H2O azeotrope by vaporization of MEK.
EXPERIMENT 2.3 (ACCORDING TO THE PRESENT IN~ENTION) lkg of crude MEK with 10 wt.~ = 0.lkg water was introduced via line 11 above the water separator in the continuously operated distillation column schematically depicted in figure 2. 0.45kg of a heterogeneous product mixture of n-hexane, MEK and water, with about 60 wt.~
n-hexane as an overhead product, was removed via line 12 and was refluxed unchanged to the column via line 14 after ,. i .
condensation. Aqueous heavy phase could also be removed via line 13, if necessary.
From the water separator in the column, 0.115kg of aqueous phase containing the total amount of water entrained with the crude MER was removed via line 17. At the column sump dry crude, MEX was obtained via line 16. The result of this dewatering is reflected by the following analysis data:
CONCENTRATION OF N-HEXANE AND WATER IN PRODUCTS
WITHDRAWN FROM SELECT TRAYS IN THE COLUMN
n-Hexane Water wt.% wt.
:~ , ' ' . : ' ' - ~ . .. .
: - :
.
Therefore, from the composition of the ternary azeotropic mixture thus formed and the solubility product resulting from this heterogeneous ternary composition, the following alternative conditions for the distillation are inferred: either a sufficient amount of water for the sep-aration of the amount of azeotropically higher-boiling by-products entrained in the distillation or a sufficient amount of azeotropically higher-boiling byproducts for the separation of the amount of water entrained in the distill-ation has to be made available.
Patent Specification GB-PS 829 424 partic-ularly describes the problem of how, during the distillation of aqueous crude SB~, the water and azeotropically higher-boiling byproducts can be separated in a column by con-trolled refluxing of aqueous phase and organic phase from the overhead product separator while maintaining a stable equilibrium in the column.
These examples make clear that the separation of water from such or similar product systems always involves a considerable effort with respect to the apparatuses or the utilities consumption.
German Patent Specification 24 07 949 outlines the formation of binary and/or ternary azeotropic mixtures is usually made use of and it is unavoidable to perform the operation with reflux ratios adjusted to the removal of water, to use separate drying columns, or to carry out dry-ing with a mole sieve in the slipstream of the column.
Therefore, it is an object of the present inven-tion to develop easily feasible or less expensive separation processes which are particularly capable of simultaneously ; 35 separating byproducts or contaminants and water.
-~ - 4 -~ 70830-14 SUMMARY OF THE IN ENTION
According to the present invention, this problem of water separation is solved by effecting, under distillation conditions in the distillation column, the separation of water from the organic substances or mixtures of substances to be purified by utilizing the presence of one or more substances boiling overhead and reducing the capacity of taking in water in the organic substances or mixtures of substances to be purified such that the water, wholly or in part, separate as the non-vaporized below the product feeding point already and is with-drawing it at the side of the distillation column.
Thus, the substance or the substances boiling overhead reduce the dissolution of water in the organic substances of mixtures of substances to be purified, or form together with water only insufficient azeotropes and thus effect overstepping of the solution limit for water in the organic substances or mixtures of substances.
According to one aspect of the present invention there ; is provided in a process for the separation of methyl tert-butyl ether f.rom a mixture comprising methyl tert-butyl ether, water and C4 hydrocarbons by fractional distillation in a distillation ~ column having means for vaporization of liquid at the base of the :; column and means for condensing vapors passing overhead therefrom and for returning a portion of the resultant condensate to the : top of the column as reflux, the improvement which comprises: -(a) introducing a feed mixture comprising C4 hydrocarbons :
~ - 5 -,, :
.
.
' :~L~ d ~ S 7 0 8 3 0--14 and methyl tert~butyl ether containing dissolved water into the distillation column at a feed point intermediate the base and top of the column, (b) distilling C4 hydrocarbon overhead with entrained water vapor, (c) condensing the distillate vapors with the formation of two immisclble liquid phases comprising a first water-rich phase and a C4-rich phase, (d) returning a portion of the C4-rich phase to the top of the column as reflux, (e) collecting a second water-rich phase and an immiscible methyl tert-butyl ether-rich phase at a point in the column below the feed point and above the base of the column, (f) withdrawing the second water-rich phase from the distillation column, and (g~ recovering methyl tert-butyl ether substantially freed from dissolved water from the base of the column.
According to a further aspect of the present invention there is provided an apparatus for performing the process defined above which comprises a distillation column suitable for azeo-tropic drying, provided with a water separator with internal or external phase separation located below the feeding tray.
; DETAILED DESCRIP~ION OF THE INVENTION
._ _ The process relates to organic substances or mixtures of substances to be purified which have only limited capability ; ~ ~of taking in water. Due to the presence of one or more substances - 5a -. , :
:
-~5~5 70830-14 reducing the dissolution of water in the organic substances or mixtures of substances to he purified, the water is eliminated.
Such products limiting the solution are at first the products to be prepared in a pure form if by overstepping the solution limit for water the water is forced to separate. This, for instance, applies to the solution limit for water in MTBE.
The solution limit for water in the product to be produced is overstepped by the - 5b -: ' , .
]oint presence of high-boiling products in the distilla-tion feed pre-venting or limiting the entraining of water into the over-head product. 3ut products limiting the solution are also those products which are contained in a concentrated form in the high-boiling overhead product and which further reduce at a suitable point in the column (below the product feeding point) the solution limit for water in the product to be produced. Such products are, for instance, n-hexane that lower the solubility of water in methyl ethyl ketone and di-sec-butyl ether that lowers the solubility of water in sec-butyl alcohol.
According to the process of the present invention, a state of permanent water saturation is maintained in the column so that the water continuously entrained with the distillation feed is inevitably eliminated due to oversatu-ration and can be withdrawn nonvaporized.
After the separation of water in the column, the residual water content in -the outflowing liquid column pro-duct is always lower than the possible water content in the ascending vaporous column product so that automatically a dry product is warranted at the column sump.
hus it has been surprisingly found that when reversing the drying principle usually employed, vaporiza-tion with azeotrope formation and condensation with decompo-sition into phases and separation of water -- be-tter results are obtained.
According to the invention, the product composi-tion which is favorable, at this point, for the insolubility of water is utilized for separating and withdrawing water in the distillation column already and this always below the ~ .
~ ~ - 6 -, ~.. ..
product feeding point. Thus, formation of water azeotropes overhead of the column can be omitted or the amount of water azeotropes overhead of the column can be lowered.
The residual water content in the liquid product stream flowing out to the stripping section of the column which results from the solution equilibrium at this water separation point, is azeotropically refluxed to the column section above the water separation point by the organic vapors formed by vaporization and ascending in the stripping section. For this return transport of water on the basis of the individually possible azeotropic compositions, a vapori-zation effort is necessary that mostly results from the separation task overlapping with the separation of other impurities. Thus, no additional vaporization effort is required for the separation of water.
In those cases where solely the separation of water is necessary, the vaporization effort has only to be adjusted to the entraining of water and to the azeotropic properties in the stripping section of the column by a cor~
respondingly forced reflux to the column.
Moreover, also by deliberate and controlled water removal at the separating tray, the water concentration in the stripping section of the column can be adjusted and maintained as required for specific separation tasks.
Thus, it is possible to withdraw the water to be 30 separated from water containing organic mixtures, wholly or n part, without additional or with a considerably lower vaporization effort, at a water separator located below the feeding point in the distillat.ion column.
~- - 7 -I'he technical realization of the princlple of the invention can be achieved by boostering a distillation column which is particularly suitable for the azeotropic drying operation by an incorporated water separator. The water separator should be installed at the point where the highest water separation has to be expected. In any case, not higher than the feeding ray or shortly below.
In this connection, it is unimportant whether an external water separator outside the column or a water sep-arating tray inside the column, is conceived as the tech-nical solution. The important thing is that all of the product outflowing to the stripping section of the distilla-tion column is conducted via the water separator. sy this prerequisite of the invention, it is warranted that the entraining of water into the stripping section of the column can always be adjusted by the solubility product on the water separating tray, irrespective of the water concentra-tion in the feedstock.
The following examples illustrate the invention by means of FIGS. 1 and 2. The examples show that by the pro-cess of the invention a significant reduction of the distil-lation effort for the separation of water is achieved or an additional distillation effort for the separation of water exceeding the actual separation task is avoided.
:
In a continuously operated distillation column schematically depicted in fig. 1, a water-containing mixture of methyl tert-~utyl ether (MTBE) and C4-hydrocarbons at a ratio of 65:35 parts-by-weight was separated by distillation at a pressure of 6 bar. The product was fed via line 1 in ':
, - 8 -- :
'YL5 the lower part of the column, 15 trays above the column sump.
Water entrained in the column was azeotropically phased out via line 2 together with the C4-hydrocarbons as overhead product, was separated after condensation of the overhead product and was withdrawn from the reflux vessel via line 3. To keep up the separation of MTBE/C4-hydro-carbons part of the overhead product was refluxed to the column via line 4. The overhead product portion contained in the feedstock was withdrawn as a distillate via line 5.
Re reflux ration R/D substantially determining the utilities consumption during this distillation is calculated from the ratio of reflux (R) to distillate (D).
In the comparison experiments 1.1 and 1.2 it is shown that when considering the simultaneous drying of water-containing feed mixtures, this reflux ratio has to be raised, in unfavorable cases, to a higher ratio -then required for the separation of MTBE and C4-hydrocarbons.
EXPERIMENT 1.1 ( COMPARI S ON ) ~ith a water portion of 9.lg entrained in 1260g of feed mixture (equal to 0.72 wt.% water) 1280g of C4 overhead product with 9.70 wt.% water were distilled off from the column by a reflux of 860g and a R/D reflux ratio of 2Ø
From this overhead product, 9.0g of water could be separated and withdrawn as a liquid phase. In the column sump 830g of C4-free MTBE with a water content of less than 0.03 wt.%
were obtained via line 6.
_ 9 _ ~ 3S~
EXPERIMENT 1.2 (COMPARISON) With a water portion of 8.5g entrained in a 1260g of feed mi~ture (equal to 0.67 wt.% water) 970g of C4 over-head product with 0.57 wt.% water were distilled off by areflux of 540g and a R/D reflux ratio of 1.2. From this overhead product, 5.5g of water could be separated and with-drawn as a liquid phase. Due to the insufficient entraining power for water of the overhead product, 830g of c4-free MTBE with a water content of 0.7 wt.% were obtained in the column sump via line 6.
In contrast thereto, as schematically depicted in figure 1, the following results can be obtained according to the invention by incorporating a water separator at a suit-able point of the column below the feeding tray and by with-drawing water via line 7:
EXPERIMENT 1.3 ACCORDING TO THE PRESENT INVENTION
. .
With a water portion of 9.8g entrained in a 1400g of feed product (equal to 0.70 wt.% water) 740g of C4 over-head product with 0.51 wt.% wa-ter were distilled off by a reflux of 250g and a R//D reflux ratio of 0.5. From this overhead product, 3.6g of water could be separated and wlth-drawn as a liquid phase. At the water separator in the column, 6.lg of water could be withdrawn through line 7. In the column sump, 910g of C4~free MTBE with a water content of less than 0.02 wt.%, were obtained through line 6.
EXPERIMENT 1.4 (ACCORDING TO THE PRESE~T INVENTION
With a water portion of 35g entrained in 1400 g of feed product (equal to 2.4 wt.% water) 740g of C4 overhead product with 0.5 wt.% water were distilled off by a reflux of 250g and a R/D reflux ratio of 0.5. From this overhead product, 3.7g of water could be separated and withdrawn as a . ~, , liquid phase. At the water separator in the column, 31.3g of water could be withdrawn through line 7. In the column sump, 910g of C4-free MTBE, with a water content of less than 0.02 wt.%, were obtained through line 6.
A crude methyl ethyl ketone (MEK) which was, for instance, produced by dehydrogenation of water-containing sec-butyl alcohol (SBA) and which contains 10 wt.~ water due to its autosolubility for water, was to be dried. Since direct separation of MEK and water is impossible due to the azeotrope formation of MEK/water, drying was to be carried out according to the state-of-the-art by azeotropic distil-lation with suitable entraining agents in a continuousl~operated distillation column schematically depicted in fig-ure 2. As azeotropic entraining agents for water, for in-stance, n-hexane or cyclohexane are used.
When feeding l.Okg of crude, MEK with 10% = 0.lkg of water via line 11, the following results were obtained.
EXPERIMENT 2.1 (COMPARISON) Using n-hexane as the azeotropic entraining agent, 2.172kg of azeotropic overhead product with 68.1 wt.%
n-hexane, 27.1 wt.% MEK and 4.8 wt.% wa*er at 56C had to be produced by vaporization and had to be removed at the column head via line 12 in order to separate 0.lkg of water or to ~ ~ 30 produce 0.9kg of dry crude MEK. After condensation and decomposition into phases 0.113kg of heavy phase with 0.lkg of water was removed therefrom via line 13, whereas 2.059kgs of light phase were refluxed to the column via line 14. At the~column sump, dry crude MEK was withdrawn via line 16.
Line 15 was not used.
: ~ ' ~:
EXPERIMENT 2.2 (COMPARISON?
Using cyclohexane as -the azeotropic entraining agent, 1.33kg of azeotropic overhead product with 56.8 wt.~
cyclohexane, 35.2 wt.% MEK and 8.0 wt.% water at 64C had to be produced by vaporization and had to be removed at the column head via line 12 in order to separate 0.lkg of water or to produce 0.9kg of dry crude MEK. After condensation and decomposition into phases 0.115kg of heavy base with 0.lkg of water was removed therefrom via line 13, whereas 1.215kgs of light phase were refluxed to the column via line 14. At the column sump dry crude MEK was withdrawn via line 16. Line 15 was not used.
In contrast thereto, when using the process of the invention, the vaporization effort can be considerably lo-wered by removing the water via line 17. The quantity of entraining agent to be employed therefor is not determined as a function of the composition of the ternary azeotrope but by the solubility product at the water separator. How-ever, the entrainer recycle has to be at least so high that the dissolved water quantity entrained from the water separ-ator in the column (depending on the MEK/entrainer ratio) can be stripped from the column as MEK/H2O azeotrope by vaporization of MEK.
EXPERIMENT 2.3 (ACCORDING TO THE PRESENT IN~ENTION) lkg of crude MEK with 10 wt.~ = 0.lkg water was introduced via line 11 above the water separator in the continuously operated distillation column schematically depicted in figure 2. 0.45kg of a heterogeneous product mixture of n-hexane, MEK and water, with about 60 wt.~
n-hexane as an overhead product, was removed via line 12 and was refluxed unchanged to the column via line 14 after ,. i .
condensation. Aqueous heavy phase could also be removed via line 13, if necessary.
From the water separator in the column, 0.115kg of aqueous phase containing the total amount of water entrained with the crude MER was removed via line 17. At the column sump dry crude, MEX was obtained via line 16. The result of this dewatering is reflected by the following analysis data:
CONCENTRATION OF N-HEXANE AND WATER IN PRODUCTS
WITHDRAWN FROM SELECT TRAYS IN THE COLUMN
n-Hexane Water wt.% wt.
4 trays below the water separator 25.9 2.6 1 3 trays below the water separator 23.7 2.9 534 trays below the water separator(*) 0.1 (*) not detectable Water and low-boiling byproducts were to be jointly separated by distillation from crude sec-butyl alco-hol (SBA) produced by conventional indirect hydration with sulfuric acid and containing about 30 percent water besides typical synthesis byproducts.
EXPERIMENT 3.1 (COMPARISON) The crude SBA was fed via line 11 to tray in the upper part of the~continuously operated distillation column schematically depicted in figure 2. A ternary azeotropic mixture of byproducts from SBA synthesis, SBA and water was removed as an overhead product via line 12 and was con-densed. During condensation, a heavy aqueous phase and a light organic phase were obtained in the reflux vessel. The water entrained with the crude SBA in the column was with-drawn with the heavy phase via line 13. The low-boiling ~ .
~-``
byproducts entrained with.the crude SBA and having a higher concentration as compared to SBA were removed via llne 15.
Most of the light organic phase was recycled to the column via line 14 in order to phase out water and to keep up the separating efficiency of the column. At the column sump, a dry SBA free from low-boiling byproducts, was removed via line 16.
From the typical composition of the overhead pro-duct thus obtained and the solution equilibrium resulting therefrom, the following distribution of quantities was inferred for the feed of e.g. lkg of crude SBA with 30.5 wt.% = 0.305kg of water:
kg_ wt.%_ Water 0.461 = 18.3 DSBE + Dimers 0.876 = 34.7 TBA 0.166 = 6.6 SBA 0.019 - 40.4 2.522 = 100.0 After decomposition into phases, the following result was obtained: !
Heav~ Phase Li ~ ase _ kg wt.% kg wt.%
Water 0.300 89.4 0.1617.4 DSBE + Dimers - - 0.87640.1 TBA 0.008 2.4 0.1587.2 SBA 0.027 8.2 0.99245.3 ~ 100.0 2.187100.0 Thus 2.564kg of azeotropic overhead product had to be produced for removing 0.305kg of water. To this end, the light upper phase, less the portion corresponding to the byproducts TBA, DSBE and dimers entrained with the crude SBA
was refluxed to the column. With an amoun-t of e.g. 3.0 wt.%
~ DSBE ~ dimers in lkg of crude SBA feed, the light phase of s 2.223kg -to be refluxed to the column would diminish by 0.075kg withdrawn through :Line 17 to 2.148kg. The water content in the stream in line 17 would be 0.005kg.
With 0.335 kg of heavy phase, the remaining 0.300kg of water was removed from the column system. Since 0.305kg of water was phased out, more overhead product had to be produced by vaporization than would have been neces- -sary for keeping up the separating efficiency in the strip-ping section of the column.
In contrast thereto, when using the process of the invention, i.e., separation and removal of water in the column, the vaporization can be limited to the separation requirements for distillative separation of by products contained besides water in the crude SBA.
EXPERIMENT 3.2 (ACCORDING TO THE PRESENT INVENTION) Like in the comparison experiment, l.Okg of crude SBA with 30.5 wt.% equal to 0.305kg of water, was fed via line 11 above the water separating tray incorporated in a continuously operated distillation column schematically depicted in figure 2.
Via line 12, e.g., 1.2kg of azeotropic overhead product, the vaporization of which ensures sufficient separ-ating efficiency in the stripping section of above distilla-tion column, was removed and condensed. During condensa-tion, 1.032kg of light phase and 0.168kg of heavy phase, having the following compositions, were o~tained in the reflux vessel:
.
~ - 15 -~., ~ ~6DS~
Heavy Phase Light Phase kg wt.% kg wt.~
Water 0.145 86.3 0.071 6.9 DSBE + Dimers - - 0.516 50.0 TsA 0.013 7.7 0.191 18.5 SBA 0.010 6.0 0.25~ 24 6 0.168 100.0 1.032 100 0 With a portion of, e.g., wt.~ DSBE + dimers in l.Okg of crude SBA feed,0.060kg with 0.004kg of water was removed from the light phase via line 15. The light phase less the 0.060kg = 0.972kg was refluxed to the column via line 14 in order to keep up the separating efficiency of the column.
With 0.168kg of heavy phase further 0.145kg of water were removed from the azeotropic overhead product via line 13. At the same time, 0.171kg of heavy phase with 0.156kg of water was withdrawn via line 17 at the water separator in the column so that a total of 0.305kg of water, which had been entrained with l.Okg of crude SBA, was re-moved from the column system. Only 0.14~kg of water thereof were vaporized and azeotropically phased out and withdrawn with 1.2kg of overhead product, whereas 0.156kg of water could be separated without additional vaporization below the crude SBA feeding tray.
By con~rol of the column temperature close to the separating tray, a regular composition of product on the ; separating tray and a regular separation of water resulting therefrom, can be maintained.
Contrary to the comparison experiment, the quan-tity to be vaporized could be lowered by more than 50 per-cent.
At the column sump dry SBA which was free from light-boiling byproducts was removed via line 16.
EXPERIMENT 3.1 (COMPARISON) The crude SBA was fed via line 11 to tray in the upper part of the~continuously operated distillation column schematically depicted in figure 2. A ternary azeotropic mixture of byproducts from SBA synthesis, SBA and water was removed as an overhead product via line 12 and was con-densed. During condensation, a heavy aqueous phase and a light organic phase were obtained in the reflux vessel. The water entrained with the crude SBA in the column was with-drawn with the heavy phase via line 13. The low-boiling ~ .
~-``
byproducts entrained with.the crude SBA and having a higher concentration as compared to SBA were removed via llne 15.
Most of the light organic phase was recycled to the column via line 14 in order to phase out water and to keep up the separating efficiency of the column. At the column sump, a dry SBA free from low-boiling byproducts, was removed via line 16.
From the typical composition of the overhead pro-duct thus obtained and the solution equilibrium resulting therefrom, the following distribution of quantities was inferred for the feed of e.g. lkg of crude SBA with 30.5 wt.% = 0.305kg of water:
kg_ wt.%_ Water 0.461 = 18.3 DSBE + Dimers 0.876 = 34.7 TBA 0.166 = 6.6 SBA 0.019 - 40.4 2.522 = 100.0 After decomposition into phases, the following result was obtained: !
Heav~ Phase Li ~ ase _ kg wt.% kg wt.%
Water 0.300 89.4 0.1617.4 DSBE + Dimers - - 0.87640.1 TBA 0.008 2.4 0.1587.2 SBA 0.027 8.2 0.99245.3 ~ 100.0 2.187100.0 Thus 2.564kg of azeotropic overhead product had to be produced for removing 0.305kg of water. To this end, the light upper phase, less the portion corresponding to the byproducts TBA, DSBE and dimers entrained with the crude SBA
was refluxed to the column. With an amoun-t of e.g. 3.0 wt.%
~ DSBE ~ dimers in lkg of crude SBA feed, the light phase of s 2.223kg -to be refluxed to the column would diminish by 0.075kg withdrawn through :Line 17 to 2.148kg. The water content in the stream in line 17 would be 0.005kg.
With 0.335 kg of heavy phase, the remaining 0.300kg of water was removed from the column system. Since 0.305kg of water was phased out, more overhead product had to be produced by vaporization than would have been neces- -sary for keeping up the separating efficiency in the strip-ping section of the column.
In contrast thereto, when using the process of the invention, i.e., separation and removal of water in the column, the vaporization can be limited to the separation requirements for distillative separation of by products contained besides water in the crude SBA.
EXPERIMENT 3.2 (ACCORDING TO THE PRESENT INVENTION) Like in the comparison experiment, l.Okg of crude SBA with 30.5 wt.% equal to 0.305kg of water, was fed via line 11 above the water separating tray incorporated in a continuously operated distillation column schematically depicted in figure 2.
Via line 12, e.g., 1.2kg of azeotropic overhead product, the vaporization of which ensures sufficient separ-ating efficiency in the stripping section of above distilla-tion column, was removed and condensed. During condensa-tion, 1.032kg of light phase and 0.168kg of heavy phase, having the following compositions, were o~tained in the reflux vessel:
.
~ - 15 -~., ~ ~6DS~
Heavy Phase Light Phase kg wt.% kg wt.~
Water 0.145 86.3 0.071 6.9 DSBE + Dimers - - 0.516 50.0 TsA 0.013 7.7 0.191 18.5 SBA 0.010 6.0 0.25~ 24 6 0.168 100.0 1.032 100 0 With a portion of, e.g., wt.~ DSBE + dimers in l.Okg of crude SBA feed,0.060kg with 0.004kg of water was removed from the light phase via line 15. The light phase less the 0.060kg = 0.972kg was refluxed to the column via line 14 in order to keep up the separating efficiency of the column.
With 0.168kg of heavy phase further 0.145kg of water were removed from the azeotropic overhead product via line 13. At the same time, 0.171kg of heavy phase with 0.156kg of water was withdrawn via line 17 at the water separator in the column so that a total of 0.305kg of water, which had been entrained with l.Okg of crude SBA, was re-moved from the column system. Only 0.14~kg of water thereof were vaporized and azeotropically phased out and withdrawn with 1.2kg of overhead product, whereas 0.156kg of water could be separated without additional vaporization below the crude SBA feeding tray.
By con~rol of the column temperature close to the separating tray, a regular composition of product on the ; separating tray and a regular separation of water resulting therefrom, can be maintained.
Contrary to the comparison experiment, the quan-tity to be vaporized could be lowered by more than 50 per-cent.
At the column sump dry SBA which was free from light-boiling byproducts was removed via line 16.
Claims (4)
1. In a process for the separation of methyl tert-butyl ether from a mixture comprising methyl. tert-butyl ether, water and C4 hydrocarbons by fractional distillation in a distillation column having means for vaporization of liquid at the base of the column and means for condensing vapors passing overhead therefrom and for returning a portion of the resultant condensate to the top of the column as reflux, the improvement which comprises:
(a) introducing a feed mixture comprising C4 hydrocarbons and methyl tert-butyl ether containing dissolved water into the distillation column at a feed point intermediate the base and top of the column, (b) distilling C4 hydrocarbon overhead with entrained water vapor, (c) condensing the distillate vapors with the formation of two immiscible liquid phases comprising a first water-rich phase and a C4-rich phase, (d) returning a portion of the C4-rich phase to the top of the column as reflux, (e) collecting a second water-rich phase and an immiscible methyl tert-butyl ether-rich phase at a point in the column below the feed point and above the base of the column, (f) withdrawing the second water-rich phase from the distillation column, and (g) recovering methyl tert-butyl ether substantially freed from dissolved water from the base of the column.
(a) introducing a feed mixture comprising C4 hydrocarbons and methyl tert-butyl ether containing dissolved water into the distillation column at a feed point intermediate the base and top of the column, (b) distilling C4 hydrocarbon overhead with entrained water vapor, (c) condensing the distillate vapors with the formation of two immiscible liquid phases comprising a first water-rich phase and a C4-rich phase, (d) returning a portion of the C4-rich phase to the top of the column as reflux, (e) collecting a second water-rich phase and an immiscible methyl tert-butyl ether-rich phase at a point in the column below the feed point and above the base of the column, (f) withdrawing the second water-rich phase from the distillation column, and (g) recovering methyl tert-butyl ether substantially freed from dissolved water from the base of the column.
2. An apparatus for performing the process according to claim 1, which comprises a distillation column for azeotropic drying, provided with a water separator with internal or external phase separation located below the feeding tray.
3. The apparatus according to claim 2, wherein the water separator is positioned at the point where the highest separation of water is to be expected.
4. The apparatus according to claim 2 or 3, wherein a water separating tray is provided which has a lateral tap as a water separator in the distillation column.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DE19863606121 DE3606121A1 (en) | 1986-02-26 | 1986-02-26 | METHOD FOR CONTINUOUSLY SEPARATING WATER FROM MIXTURES WITH ORGANIC SUBSTANCES |
| DEP3606121.2-45 | 1986-02-26 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1305445C true CA1305445C (en) | 1992-07-21 |
Family
ID=6294941
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000530570A Expired - Fee Related CA1305445C (en) | 1986-02-26 | 1987-02-25 | Process for the continuous separation of water from mixtures with organic substances |
Country Status (16)
| Country | Link |
|---|---|
| US (1) | US4943354A (en) |
| EP (1) | EP0234508B1 (en) |
| JP (1) | JPS62216601A (en) |
| CN (1) | CN87100934A (en) |
| AT (1) | ATE95716T1 (en) |
| AU (1) | AU6928987A (en) |
| CA (1) | CA1305445C (en) |
| DD (1) | DD254526A5 (en) |
| DE (2) | DE3606121A1 (en) |
| DK (1) | DK96387A (en) |
| ES (1) | ES2044846T3 (en) |
| FI (1) | FI870575A (en) |
| IN (1) | IN169182B (en) |
| NO (1) | NO870644L (en) |
| PL (1) | PL264303A1 (en) |
| ZA (1) | ZA87664B (en) |
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| JPH01176101A (en) * | 1987-12-29 | 1989-07-12 | Nec Corp | Directional coupler |
| DE3905786A1 (en) * | 1989-02-24 | 1990-08-30 | Wipf Ag Verpackungen | METHOD AND DEVICE FOR SEPARATING DIACETYL-CONTAINING MIXTURES FROM METHYL ETHYL KETONE, ETHYL ACETATE, ETHANOL AND WATER, AND, WHERE APPROPRIATE, TOLUENE AND N-HEXANES |
| US5157163A (en) * | 1991-10-03 | 1992-10-20 | Texaco Chemical Company | Purification of methyl tertiary-butyl ether |
| US5151160A (en) * | 1992-04-06 | 1992-09-29 | Lloyd Berg | Dehydration of 2-methoxyethanol by extractive distillation |
| JP3288995B2 (en) * | 1999-09-22 | 2002-06-04 | 淳一 岩村 | Separation method for refractory organic substances |
| JP4549324B2 (en) * | 2006-08-04 | 2010-09-22 | 株式会社日本触媒 | Method for producing dehydration reaction product |
| BRPI0805249B1 (en) * | 2008-12-12 | 2021-05-18 | Petróleo Brasileiro S/A - Petrobras | method for control of instability in dewatering tower in fluid catalytic cracking units and in delayed coking units |
| US8222466B2 (en) | 2010-02-02 | 2012-07-17 | Celanese International Corporation | Process for producing a water stream from ethanol production |
| US8569551B2 (en) * | 2010-05-07 | 2013-10-29 | Celanese International Corporation | Alcohol production process integrating acetic acid feed stream comprising water from carbonylation process |
| JP6076579B2 (en) * | 2010-06-23 | 2017-02-08 | 株式会社ダイセル | Operation method of distillation tower |
| US8859827B2 (en) | 2011-11-18 | 2014-10-14 | Celanese International Corporation | Esterifying acetic acid to produce ester feed for hydrogenolysis |
| DE102010042774A1 (en) * | 2010-10-21 | 2012-04-26 | Evonik Oxeno Gmbh | Process for the purification of MTBE-containing mixtures and for the production of isobutene by cleavage of MTBE-containing mixtures |
| US8927780B2 (en) | 2011-04-26 | 2015-01-06 | Celanese International Corporation | Process for removing aldehydes from ethanol reaction mixture |
| US8461399B2 (en) | 2011-04-26 | 2013-06-11 | Celanese International Corporation | Separation process having an alcohol sidestream |
| US8748675B2 (en) | 2011-06-16 | 2014-06-10 | Celanese International Corporation | Extractive distillation of crude alcohol product |
| WO2013019236A1 (en) * | 2011-08-03 | 2013-02-07 | Celanese International Corporation | Process for recovering ethanol in a side draw distillation column |
| US8877986B2 (en) | 2011-08-03 | 2014-11-04 | Celanese International Corporation | Process for recovering alcohol |
| US9024089B2 (en) | 2011-11-18 | 2015-05-05 | Celanese International Corporation | Esterification process using extractive separation to produce feed for hydrogenolysis |
| US8853468B2 (en) | 2011-11-18 | 2014-10-07 | Celanese International Corporation | Vapor esterification method to produce ester feed for hydrogenolysis |
| US8829249B2 (en) | 2011-11-18 | 2014-09-09 | Celanese International Corporation | Integrated esterification and hydrogenolysis process for producing ethanol |
| US8829251B2 (en) | 2011-11-18 | 2014-09-09 | Celanese International Corporation | Liquid esterification method to produce ester feed for hydrogenolysis |
| US8802901B2 (en) | 2011-11-18 | 2014-08-12 | Celanese International Corporation | Continuous ethyl acetate production and hydrogenolysis thereof |
| US8748673B2 (en) | 2011-11-18 | 2014-06-10 | Celanese International Corporation | Process of recovery of ethanol from hydrogenolysis process |
| CN103946200A (en) | 2011-11-22 | 2014-07-23 | 国际人造丝公司 | Esterifying an ethanol and acetic acid mixture to produce an ester feed for hydrogenolysis |
| US9029614B2 (en) | 2011-12-14 | 2015-05-12 | Celanese International Corporation | Phasing reactor product from hydrogenating acetic acid into ethyl acetate feed to produce ethanol |
| US8907139B2 (en) | 2011-12-28 | 2014-12-09 | Celanese International Corporation | Process for acetal removal in the purification of a crude ethanol product |
| CN104039448B (en) | 2012-01-06 | 2016-11-16 | 国际人造丝公司 | There is the hydrogenation catalyst of Co-modified supports |
| US9024086B2 (en) | 2012-01-06 | 2015-05-05 | Celanese International Corporation | Hydrogenation catalysts with acidic sites |
| US8772553B2 (en) | 2012-10-26 | 2014-07-08 | Celanese International Corporation | Hydrogenation reaction conditions for producing ethanol |
| US8957262B2 (en) | 2012-11-20 | 2015-02-17 | Celanese International Corporation | Olefin hydration for hydrogenation processes |
| US9000237B2 (en) | 2012-12-20 | 2015-04-07 | Celanese International Corporation | Ethanol refining process using intermediate reboiler |
| US8975451B2 (en) | 2013-03-15 | 2015-03-10 | Celanese International Corporation | Single phase ester feed for hydrogenolysis |
| US8975450B2 (en) | 2013-03-15 | 2015-03-10 | Celanese International Corporation | Ethanol and ethyl acetate production using an acetic acid and acetic anhydride mixed feed |
| US8926718B2 (en) | 2013-03-15 | 2015-01-06 | Celanese International Corporation | Thermochemically produced ethanol compositions |
| CN103333056B (en) * | 2013-07-17 | 2015-07-08 | 凯瑞环保科技股份有限公司 | Method and device for deeply removing sulfide in MTBE |
| CN104876785A (en) * | 2015-06-10 | 2015-09-02 | 中国海洋石油总公司 | Process and device for producing MTBE (methyl tert-butyl ether)/butene-1 from remaining C4 |
Family Cites Families (13)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US2854385A (en) * | 1953-12-24 | 1958-09-30 | Melle Usines Sa | Treatment of acetic acid and mixtures thereof |
| US3031384A (en) * | 1959-09-15 | 1962-04-24 | Exxon Research Engineering Co | Separation of acetone, alcohol and water |
| FR1399653A (en) * | 1964-04-06 | 1965-05-21 | Melle Usines Sa | Continuous process for the preparation of functional alcohol derivatives |
| FR1573026A (en) * | 1968-01-31 | 1969-07-04 | ||
| GB1308718A (en) * | 1970-07-01 | 1973-03-07 | Sir Soc Italiana Resine Spa | Method of separating vinyl acetate from liquid mixtures |
| IT956765B (en) * | 1972-06-22 | 1973-10-10 | Montedison Spa | PROCEDURE FOR THE PURIFICATION OF 1 3 DIOXOLAN |
| DE2539737C2 (en) * | 1975-09-06 | 1982-02-25 | Edeleanu Gmbh, 6000 Frankfurt | Process for the continuous recovery of thermally unstable solvent mixtures |
| DE2720405A1 (en) * | 1977-05-06 | 1978-11-09 | Agway Inc | Dewatering unprocessed sewage sludge - by using urea or ammonium or potassium salts |
| JPS5941864B2 (en) * | 1977-07-27 | 1984-10-11 | 大日本印刷株式会社 | Stretch film for food packaging |
| FR2449666A1 (en) * | 1979-02-22 | 1980-09-19 | Inst Francais Du Petrole | PROCESS FOR ISOLATING METHYLTERTIOBUTYLETHER FROM METHANOL REACTION PRODUCTS WITH A CUT OF C4 HYDROCARBONS CONTAINING ISOBUTENE |
| EP0044409B1 (en) * | 1980-06-20 | 1984-01-11 | Asahi Kasei Kogyo Kabushiki Kaisha | Process for purifying methyl methacrylate |
| US4490563A (en) * | 1981-08-28 | 1984-12-25 | Phillips Petroleum Company | Ether recovery |
| DE3150755A1 (en) * | 1981-12-22 | 1983-06-30 | Deutsche Texaco Ag, 2000 Hamburg | "METHOD FOR SEPARATING METHANOL FROM THE REACTION PRODUCTS INCLUDING METHANOL FROM C (ARROW DOWN) 4 (ARROW DOWN) TO C (ARROW DOWN) 7 (ARROW DOWN) 7 (ARROW DOWN)" |
-
1986
- 1986-02-26 DE DE19863606121 patent/DE3606121A1/en not_active Withdrawn
-
1987
- 1987-01-29 ZA ZA87664A patent/ZA87664B/en unknown
- 1987-02-11 FI FI870575A patent/FI870575A/en not_active Application Discontinuation
- 1987-02-18 NO NO870644A patent/NO870644L/en unknown
- 1987-02-19 ES ES87102380T patent/ES2044846T3/en not_active Expired - Lifetime
- 1987-02-19 EP EP87102380A patent/EP0234508B1/en not_active Expired - Lifetime
- 1987-02-19 DE DE87102380T patent/DE3787737D1/en not_active Expired - Fee Related
- 1987-02-19 AT AT87102380T patent/ATE95716T1/en not_active IP Right Cessation
- 1987-02-24 DD DD87300140A patent/DD254526A5/en not_active IP Right Cessation
- 1987-02-25 CA CA000530570A patent/CA1305445C/en not_active Expired - Fee Related
- 1987-02-25 DK DK096387A patent/DK96387A/en not_active Application Discontinuation
- 1987-02-25 CN CN198787100934A patent/CN87100934A/en active Pending
- 1987-02-25 PL PL1987264303A patent/PL264303A1/en unknown
- 1987-02-26 JP JP62041568A patent/JPS62216601A/en active Granted
- 1987-02-26 AU AU69289/87A patent/AU6928987A/en not_active Abandoned
- 1987-02-26 IN IN133/MAS/87A patent/IN169182B/en unknown
-
1989
- 1989-03-17 US US07/326,493 patent/US4943354A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DD254526A5 (en) | 1988-03-02 |
| NO870644D0 (en) | 1987-02-18 |
| AU6928987A (en) | 1987-08-27 |
| JPS62216601A (en) | 1987-09-24 |
| ATE95716T1 (en) | 1993-10-15 |
| ZA87664B (en) | 1987-09-30 |
| JPH0559764B2 (en) | 1993-08-31 |
| US4943354A (en) | 1990-07-24 |
| DE3787737D1 (en) | 1993-11-18 |
| NO870644L (en) | 1987-08-27 |
| DK96387A (en) | 1987-08-27 |
| EP0234508B1 (en) | 1993-10-13 |
| FI870575A (en) | 1987-08-27 |
| DE3606121A1 (en) | 1987-08-27 |
| IN169182B (en) | 1991-09-14 |
| CN87100934A (en) | 1987-11-18 |
| FI870575A0 (en) | 1987-02-11 |
| EP0234508A3 (en) | 1988-09-14 |
| EP0234508A2 (en) | 1987-09-02 |
| PL264303A1 (en) | 1988-04-14 |
| DK96387D0 (en) | 1987-02-25 |
| ES2044846T3 (en) | 1994-01-16 |
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